Selective hydrogenation of alkynes

ABSTRACT

AN IMPROVED PROCESS FOR SELECTIVELY HYDROGENATING ACETYLENIC IMPURITES IN AN ISOPRENE- OR BUTADIENE- CONTAINING STREAM WHEREBY FROM 0.7 TO 15 VOLUME PERCENT CO IS UTILIZED DURING NORMAL HYDROGENATION OVER A COPPERBASED CATALYST.

United States Patent 3,634,536 SELECTIVE HYDROGENATION 0F ALKYNES Ludo K. Frevel, Midland, and Leonard J. Kressley, Saginaw, Mich., assignors to The Dow Chemical Company, Midland, Mich. No Drawing. Filed Apr. 27, 1970, Ser. No. 32,378 Int. Cl. C07c 7/00 US. Cl. 260-681.5 R 2 Claims ABSTRACT OF THE DISCLOSURE An improved process for selectively hydrogenating acetylenic impurites in an isopreneor butadienecontaining stream whereby from 0.7 to 15 volume percent CO is utilized during normal hydrogenation over a copperbased catalyst.

BACKGROUND OF THE INVENTION It is well known that a variety of processes for the pyrolysis of petroleum fractions produce relatively large quantities of diolefins, particularly conjugated diolefins, The diolefin-containing mixtures so obtained also contain other hydrocarbons. It is a common practice to fractionate this mixture to obtain, for instance, a fraction containing compounds such as butadiene-1,3, isobutane, isobutylene, n-butylene-l, n-butane, n-butylene-2, methylacetylene, ethylacetylene, vinylacetylene, and the like. Dehydrogenation of n-butane or n-butenes or both and 2-methyl butane or 2-methyl butenes to butadiene and isoprene, respectively, also produces some 0. and C acetylenic compounds which must be removed from the diene before use in polymerization reactions.

It has been the experience of the art that, while the diolefin content of each fraction may be concentrated by usual purification techniques, the acetylenic hydrocarbons and other highly unsaturated hydrocarbon impurities of about the same boiling point are extremely difficult to separate.

It is the current practice of industry to selectively hydrogenate the acetylenic and other unsaturated impurities in order to render them more amenable to standard re moval procedures. However, two problems have been experienced by the art:

(1) A significant amount of butadiene or isoprene is lost during the selective hydrogenation; and

(2) The process, as practiced, is limited in the amount of acetylenics which may be removed, i.e., final acetylenic concentrations much below 100 p.p.m. by weight are difficult to achieve without excessive conversion of the diene to a monoolefin or alkane.

SUMMARY OF THE INVENTION It has now been discovered that it is possible, in accordance with the method of the present invention, to correct the problems experienced by the art associated with the selective hydrogenation of acetylenic impurities in an isopreneor butadiene-containing stream.

It is an object of the present invention to selectively hydrogenate the acetylenic compounds in an isopreneor butadiene-containing stream without a material loss of the diene.

It is a further object to provide a process which effectively hydrogenates a greater proportion of acetylenic compounds than has heretofore been possible without a material loss of isoprene or butadiene.

Therefore, in accordance with the method of the present invention, it is now possible to reduce the concentration of C acetylenes to a level as low as about 500 p.p.m. by selective hydrogenation, said process comprising passing an isopreneor butadiene-containing stream with excess hydrogen, said stream containing up to about 1 weight percent of C acetylenes, over a copper-based catalyst, said hydrogenation to occur in the presence of from 0.7 to 15 volume percent of CO.

Further, it is now possible, also in accordance-with the present invention, to reduce the concentration of C acetylenes to a level even as low as about 10 ppm. or less by selective hydrogenation, said process comprising passing an isopreneor butadiene-containing stream with excess hydrogen, said stream containing 50 to 1000 p.p.m. of C acetylenes, over a copper-based catalyst, said hydrogenation to occur in the presence of from 3% to 15 volume percent of CO.

The catalytic hydrogenation conditions and catalysts generally suitable for the method of this invention are detailed in US. Pat. 2,426,604 (1947), the specification of which is hereby expressly incorporated by reference. The streams which are suitable herein as feeds comprise those which contain isoprene or butadiene-1,3, and other hydrocarbons, such as isobutane, isobutylene, n-butylene- 1, n butane and n-butylene-2; up to 1 weight percent of C acetylenic compounds, such as acetylene, methylacetylene, vinylacetylene, ethylacetylene, and the like; and, other hydrocarbon compounds such as alkanes and cycloalkanes, such as n-pentane, isopentane, neopentane, cyclohexane, and the like.

The catalysts which are suitable for the process of this invention are prepared so as to contain between and 99.9 (preferably between and 97) percent by weight of copper and between 15 and 0.1 (preferably between 10 and 3) percent of another metal, the oxide of which is reducible to a lower valence state with hydrogen at temperatures below 550 C. Examples of such metals include chromium, cobalt, manganese, nickel, vanadium, titanium, molybdenum, cadmium, zinc, silver, and the like, and also mixtures of such metals.

The catalysts are preferably employed in dispersed form on a substantially inert carrier material such as aluminum silicate, brick, stoneware, pumice, porous silica, and the like. Generally, this supported catalyst is prepared so as to contain from 10 to 30 percent by weight of the mixture of metals, but it may contain such metals in smaller or greater proportions. The above incorporated patent includes detailed instructions as to the various methods of preparing said catalyst.

The reaction conditions which are most suited for the method of this invention involve generally a 4 to 7 (preferably about 6) fold excess of hydrogen with respect to the concentration of acetylenes in the feed, and a space velocity of 300-1000, preferably about 600.

SPECIFIC EMBODIMENTS Example I The reactor was a glass tube (1.5 centimeters ID. by 10.5 centimeters long) with a 3 millimeter O.D. thermocouple well centered concentrically the length of the tube. The internal volume of the reactor was 18.5 milliliters. It was loaded with 9.827 grams of catalyst. The catalyst contained 14 weight percent copper and 0.7 weight percent nickel on a siliceous support.

The reactor tube was inserted into a thermostatic heating unit, and the reactor brought to the indicated temperature. The feed stream 'was vaporized and mixed with hydrogen and carbon monoxide, and the mixture passed through the heated reactor. The efiiuent was condensed in a Dry Ice trap, the condensate being analyzed by gas liquid chromatography.

The specific conditions, results and analytical data are contained in the following table:

Without With 00, 048 vol, percent With 00, 5.47 vol, percent With 00, 0,74 vo1 percent Mole percent Mole percent Mole percent Mole percent Feed Eff. Percent 1 Feed Eff; Percent Feed Eff. Percent Percent Efi Percent d: l b t i il butanesu 8.0 8. 3 9. 29 9. 20 9. 29 9. 08 9. 17 9. 13

Total butenes--- 41. 8 42. 7 53.10 54. 22 53. 53. 21 52. 45 52.17

1,3-butadiene 50.2 49. 0 2. 4 37. 45 36. 39 2- 8 37- 45 37. 65 +0. 27 38. 38. 52 +0. 84

Total O4 (p.p m.)-- (918) (14) (1, 215) (Nil) (1,215) (Nil) (3, 300) (590) Outlet temp., C--- 1797 018702 018702 0155i8 H v 1 ercent 0. 8

1 Percent change (plus or minus) in butadiene, 2 Efiluent.

Example II A further experiment under similar circumstances as above was conducted. The feed analysis was as follows:

Liquid percent Isobutane 1.4 Isobutylene 8.5 n-Butylene-l 27.2 Butadiene-1,3 50.8 n-Butane 8.2 n-Butylene-Z L.B. 3.9

Wt. percent Methyl acetylene .0033 Ethyl acetylene .0076 Vinyl acetylene .0795

A semi-continuous run was made with the object of demonstrating the effect of CO on the level of acetylenes remaining in the feed after hydrogenation.

210 ml./min. of the above hydrocarbons and 7.5 ml./ min. of a '75%/25%-argon/hydrogen mixture were passed through the reaction chamber described above at a temperature of from 178-181 C. At the beginning about 12 volume percent of CO was also fed, and the acetylene levels monitored. After a period of time the CO flow was shut off, and the acetylenes monitored further. Finally 12 volume percent of CO was again admitted, and, once again, the acetylenes monitored.

It was noted that the acetylene concentration in the efliuent was generally about 5 times greater when the CO was not present during hydrogenation, concentrations as low as 7 p.p.m. being realized with the addition of CO.

An isoprene-containing stream would have the acetylenic impurities therein selectively hydrogenated similarly as above.

We claim:

1. In the process for the selective hydrogenation of 'acetylenic impurities in an isopreneor butadiene-con- References Cited UNITED STATES PATENTS 2/ 1963 Frevel et al. 260677 PA'UL M. COUGHLAN, JR., Primary Examiner V. OKEEFE, Assistant Examiner U.S. C1. X.R. 

